Drilling fluids, also referred to as drilling muds, are commonly used to drill oil and gas wells. Drilling fluids are mixtures of oil, brine, emulsifiers and solids to create the properties needed to provide borehole stability and remove drilled solids, also referred to as cuttings, from the well. These fluids provide excellent drilling performance, but they are expensive, and disposal is regulated. While drilling oil and gas wells, solids control equipment including shale shakers, mud cleaners, centrifuges, etc., is used to remove drilled solids from the drilling mud. As drilled solids are removed, some of the drilling fluid is removed with them. When the well is completed, the removed solids must be disposed of. Most government disposal regulations specify a maximum amount of oil on the drilled solids that must be met before disposal can occur.
The percentage of hydrocarbons on cuttings, also referred to as oil-on-cuttings, can be used to determine how much drilling fluid is lost with the drilled cuttings as they are removed. Currently, many service providers do not even test for this value. Instead, they simply make an assumption based upon the total volume of fluid they have accumulated during the day.
The oil-on-cuttings can also be used to determine compliance with local environmental regulations before the disposal of the solids. Currently, service providers use a retort to determine this value. Retorts can be used to measure the volume percentages of oil, water and solids in a drilled solids sample. A retort is a well-known device that heats a sample to separate fluids from solids by evaporation, resulting in percentage solid, percentage water and percentage oil. This test takes hours to set-up and complete, has a high degree of inaccuracy, and therefore is only used when necessary. Typically, only two or three retorts are run during a 24-hour period, despite waste being discharged during the entire 24-hour period. Monitoring oil-on-cuttings more frequently and using it to optimize drilling fluid dilution volumes and solids control equipment is desired to reduce overall drilling costs. Furthermore, more accurate and more frequent measurement of the oil-on-cuttings value is desired to ensure environmental regulatory compliance.
Another known way to measure oil-on-cuttings is using a device known as the InfraCal® TOG/Hydrocarbon Analyzer (available from Spectro Scientific, previously Wilks Enterprise, Inc.) for measuring total oil and grease (TOG) and total petroleum hydrocarbon (TPH) levels. This device requires a solvent extraction and analysis by infrared spectroscopy with attenuated total reflection (ATR) after removal of the solvent.
There still exists a need for a quicker and more accurate method for estimating total petroleum hydrocarbons concentration in drilling cuttings without using solvent.